Display device

ABSTRACT

A display device which provides reliable connection between a semiconductor device and a printed circuit board includes a display panel, a printed circuit board disposed close to the display panel, and a semiconductor device of a film carrier type which is disposed to lie between the display panel and the printed circuit board, and terminals of the semiconductor device are respectively connected by an anisotropic conductive film to terminals of the printed circuit board that are disposed in opposition to the respective terminals of the semiconductor device.

BACKGROUND OF THE INVENTION

The present invention relates to an active matrix type liquid crystaldisplay device.

An active matrix type liquid crystal display device includes transparentsubstrates disposed in opposition to each other with a liquid crystalmaterial interposed therebetween; gate signal lines disposed so as toextend in the x direction and to be juxtaposed in the y direction; drainsignal lines disposed so as to extend in the y direction and to bejuxtaposed in the x direction, the gate signal lines and the drainsignal lines being formed on a liquid-crystal-Side surface of either oneof the transparent substrates; and pixel areas, each formed by an areasurrounded by adjacent ones of the gate signal lines and adjacent onesof the drain signal lines.

These pixel areas are disposed in matrix form, and a liquid crystaldisplay region is formed by an aggregation of the pixel areas.

Each of the pixel areas is provided with a switching element, which isoperated by a scanning signal supplied from one of the adjacent gatesignal lines, and a pixel electrode, which is supplied with a videosignal from one of the adjacent drain signal lines via the switchingelement.

This pixel electrode is constructed to control the opticaltransmissivity of the liquid crystal material by causing an electricfield to be generated between the pixel electrode and a counterelectrode formed on either one of the transparent substrates.

The gate signal lines and the drain signal lines are disposed so as toextend to the outside of the liquid crystal display region of the liquidcrystal display device, and scanning signals applied to the gate signallines are supplied from a scanning signal driver circuit connected tothe gate signal lines, while video signals applied to the drain signallines are supplied from a video signal driver circuit connected to thedrain signal lines.

The liquid crystal display device has a plurality of scanning signaldriver circuits and video signal driver circuits, and mutually adjacentones of the scanning signal lines or drain signal lines are grouped andeach group is assigned to one scanning signal driver circuit or onevideo signal driver circuit.

One construction of such a driver circuit includes a semiconductordevice formed by a so-called tape carrier method, which has aconstruction such that a semiconductor chip is mounted on a film-likesubstrate and interconnection layers, which are respectively connectedto the bumps of the semiconductor chip, are formed along a surface ofthe-film-like substrate, and the extending ends of the respectiveinterconnection layers are connected to a terminal at each end of theinterconnection layers.

Solder is used for the connection between the input terminals of thesemiconductor device and terminals of the printed circuit board, whereasthe connection between the output terminals of the semiconductor deviceand terminals of the liquid crystal display panel is provided by aso-called anisotropic conductive film ACF.

SUMMARY OF THE INVENTION

However, in the recent trends toward far higher resolutions and far morecolors of liquid crystal display devices, it has been pointed out that,as the number of input terminals and the number of output terminalsincrease in a semiconductor device, a problem, such as a short betweenadjacent terminals, occurs during the connection between the terminalsof the semiconductor device and those of a printed circuit board.

The object of the present invention is to solve such a problem and toprovide a liquid crystal display device with reliable connection betweena semiconductor device and a printed circuit board.

Representative method to solve the above-mentioned problem is to providea liquid crystal display device according to the invention thatincludes, for example, a liquid crystal display panel, a printed circuitboard, and a semiconductor device of a tape carrier type, which isdisposed to lie between the liquid crystal display panel and the printedcircuit board, and wherein input terminals of the semiconductor deviceare respectively connected by an anisotropic conductive film toterminals of the printed circuit board that are disposed in oppositionto the respective input terminals of the semiconductor device.

In a liquid crystal display device constructed in this manner, it ispossible to prevent a short circuit condition between adjacent terminalsduring the connection between the input terminals of the semiconductordevice and the terminals of the printed circuit board, even if the inputterminals of the semiconductor device become large in number and narrowin pitch.

The reason for this is that the size of conductive beads contained inthe anisotropic conductive film ACF is small, and adjacently disposedterminals are not electrically connected by the conductive beads at thetime when the semiconductor device is secured to the printed circuitboard by thermocompression bonding via the anisotropic conductive filmACF.

On the other hand, in the case of using solder to connect the terminalsof the semiconductor device and those of the printed circuit board, thesolder spreads horizontally during bonding of the semiconductor deviceto the printed circuit board. This spread of solder reaches otheradjacent terminals and causes a short circuit between adjacentterminals.

The invention mentioned in detail in the specification can solve thisshort circuit.

These and other objects, features and advantages of the presentinvention will become more apparent from the following description whentaken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will become more readily appreciated and understood fromthe following detailed description of preferred embodiments of theinvention, when taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a plan view showing a portion of an embodiment of the liquidcrystal display device according to the invention;

FIG. 2 is an equivalent circuit diagram of an embodiment of the liquidcrystal display device according to the invention;

FIG. 3 is a plan view showing an embodiment of a pixel of the liquidcrystal display device according to the invention;

FIG. 4 is a cross-sectional view taken along line IV-IV of FIG. 3;

FIG. 5 is a graph showing an advantage of the liquid crystal displaydevice according to the invention;

FIG. 6 is a plan view showing the essential portion of anotherembodiment of the liquid crystal display device according to theinvention;

FIG. 7 is a plan view showing a portion of another embodiment of theliquid crystal display device according to the invention;

FIG. 8 is a plan view showing a portion of another embodiment of theliquid crystal display device according to the invention;

FIG. 9 is a plan view showing a portion of another embodiment of theliquid crystal display device according to the invention; and

FIG. 10 is a plan view showing a portion of another embodiment of theliquid crystal display device according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

Preferred embodiments of a liquid crystal display device according tothe invention will be described below with reference to the accompanyingdrawings.

Embodiment 1

Equivalent Circuit

FIG. 2 is a view showing the equivalent circuit of a liquid crystaldisplay device according to the invention. In FIG. 2, the circuitdiagram is arranged to correspond to the actual geometrical layout ofthe liquid crystal display device. Transparent substrate SUB1 isdisposed in opposition to another transparent substrate SUB2 with aliquid crystal material interposed therebetween.

Gate signal lines GL and drain signal lines DL are formed on aliquid-crystal-side surface of the transparent substrate SUB1. The gatesignal lines GL are disposed so as to extend in the x direction and tobe juxtaposed in the y direction. The drain signal lines DL areinsulated from the gate signal lines GL and are disposed so as to extendin the y direction and to be juxtaposed in the x direction. Rectangularareas, each of which is surrounded by adjacent ones of the gate signallines GL and adjacent ones of the drain signal lines DL constitute pixelareas, respectively, and a liquid crystal display region AR is formed byan aggregation of these pixel areas.

A thin film transistor TFT and a pixel electrode PX are formed in eachof the pixel areas. The thin film transistor TFT is driven by supply ofa scanning signal (voltage) from one of the adjacent gate signal linesGL, and a video signal (voltage) is supplied to the pixel electrode PXfrom one of the adjacent drain signal lines DL via the thin filmtransistor TFT.

A capacitance element Cstg is formed between the pixel electrode PX anda counter voltage signal line CL, which will be described later, tostore a video signal supplied to the pixel electrode for a along timewhen the thin film transistor TFT is turned off.

The pixel electrodes PX in each of the pixel areas are arranged adjacentto the counter electrode CT to generate an electric field between therespective pixel electrodes PX and counter electrodes CT. The opticaltransmissivity of the liquid crystal is controlled by the electricfields, which have a substantial component parallel to the transparentsubstrate SUB1.

One end of each of the gate signal lines GL is formed to extend from theliquid crystal display region AR to one side (in FIG. 2, the left-handside) of the transparent substrate SUB1, and this extending portion isformed as a terminal part GTM, which is connected to an output terminalof a vertical scanning driver circuit V.

In addition, one end of each of the drain signal lines DL is formed toextend from the liquid crystal display region AR to one side (in FIG. 2,the top side) of the transparent substrate SUB 1, and this extendingportion is formed as a terminal part DTM, which is connected to anoutput terminal of a video signal driver circuit He.

A plurality of vertical scanning driver circuits V are disposed so as tobe aligned in the y direction as viewed in FIG. 2; and, a predeterminednumber of mutually adjacent ones of the gate signal lines GL aregrouped, and a respective one of the vertical scanning driver circuits Vis assigned to the predetermined number of gate signal lines GL of eachrespective group.

Similarly, a plurality of video signal driver circuits He are disposedso as to be aligned in the x direction, as viewed in FIG. 2; and, apredetermined number of mutually adjacent ones of the drain signal linesDL are grouped, and a respective one of the video signal driver circuitsHe is assigned to the predetermined number of drain signal lines DL ofeach respective group.

FIG. 1 is a plan view showing the details of the video signal drivercircuits He, by way of example, and this figure shows two juxtaposedones of the video signal driver circuits He.

Each of the video signal driver circuits He is made up of asemiconductor device manufactured by a so-called tape carrier method. Asemiconductor chip IC is mounted on a film-like substrate SUB0, and theinput bumps of the semiconductor chip IC are respectively led out toinput terminals IT via interconnection layers WL formed on a surface ofthe substrate SUB0, while the output bumps of the semiconductor chip ICare respectively led out to output terminals OT via the interconnectionlayers WL.

The input terminals IT are formed so as to be juxtaposed along one sideportion of the substrate SUB0, while the output terminals OT are formedso as to be juxtaposed along the other side portion opposite to the oneside portion of the substrate SUB0. The input terminals IT are smallerin number than the output terminals OT, and, accordingly, the width ofeach of the input terminals IT is slightly larger than that of each ofthe output terminals OT.

In each of the video signal driver circuits He constructed in thismanner, the respective output terminals OT are connected to the drainterminal parts DTM of the corresponding drain signal lines DL via ananisotropic conductive film ACF, and the respective input terminals ITare connected via an anisotropic conductive film ACF to correspondingterminals of a printed circuit board PCB (in this specifications theterm “liquid crystal display panel” indicates a construction whichincludes the transparent substrates SUB1 and SUB2 disposed with theliquid crystal material interposed therebetween, as well as materiallayers formed on the surfaces of each of the transparent substrates SUB1and SUB2).

A circuit for driving the video signal driver circuits He is mounted onthe printed circuit board PCB, and signals which also include electricpower are inputted to the video signal driver circuits He via theprinted circuit board PCB.

Each of the anisotropic conductive films ACF is made of a resin filmwhich contains a multiplicity of minute conductive beads. The videosignal driver circuits He are positioned with respect to, for example,the printed circuit board PCB via these anisotropic conductive films ACFand are secured to the printed circuit board PCB by thermocompressionbonding, whereby each terminal of the video signal driver circuits He iselectrically connected to its opposed terminal of the printed circuitboard PCB via the conductive beads.

The vertical scanning driver circuits V only differ from the videosignal driver circuits He in the circuit constructions of semiconductorchips, and are constructed in a manner similar to the above-describedone.

Construction of Pixel

FIG. 3 is a plan view showing one example of one of the pixels of theliquid crystal display device according to the invention. FIG. 4 shows across-sectional view taken along line IV-IV of FIG. 3.

FIG. 3 is a view of the construction of one pixel on theliquid-crystal-side surface of the transparent substrate SUB1, which isone of the transparent substrates SUB1 and SUB2 disposed in oppositionto each other with the liquid crystal material interposed therebetween.The pixels are arranged in matrix form. Accordingly, each of otherpixels, which are respectively positioned on the top, bottom, right andleft sides of the pixel area shown in FIG. 3 also has a similarconstruction.

A gate signal line GL, which is disposed so as to extend in the xdirection of FIG. 3, is formed on the surface of the transparentsubstrate SUB1 on the bottom side of the illustrated pixel area.

This gate signal line GL is formed to surround the pixel area togetherwith a gate signal line (not shown) which corresponds to a pixel areapositioned on the top side of the pixel area, a drain signal line DLwhich will be described later, and a drain signal line (not shown) whichcorresponds to a pixel area positioned on the right-hand side of thepixel area.

A counter voltage signal line CL, which is disposed so as to extend inthe x direction in FIG. 3, is formed in the middle of the pixel area.This counter voltage signal line CL is formed, for example, in the sameprocess as the gate signal line GL. In this case, the material of thecounter voltage signal line CL is the same as that of the gate signalline GL.

The counter voltage signal line CL is formed integrally with the counterelectrode CT, and a plurality of counter electrodes CT are formed so asto extend in the upward and downward directions (in the y direction inFIG. 3) from the counter voltage signal line CL and to be juxtaposed inthe x direction.

Each of the counter electrodes CT is formed to have a zigzag shape inits extension direction. This construction will be described later indetail in connection with the pixel electrode PX.

An insulating film GI made of, for example, SiN is formed to cover thegate signal line GL and the counter voltage signal line CL (the counterelectrodes CT) on the surface of the transparent substrate SUB1, onwhich the gate signal line GL and the counter voltage signal line CL(the counter electrodes CT) are formed in the above-described manner.

This insulating film GI has the function of an interlayer insulatingfilm disposed between the drain signal line DL (which will be describedlater) and the gate signal line GL, as well as the counter voltagesignal line CL, the function of a gate insulating film with respect tothe thin film transistor TFT, which will be described later, and thefunction of a dielectric film with respect to the capacitance elementCstg, which will be described later.

A semiconductor layer AS, which is made of, for example, amorphous Si(a-Si), is formed on the surface of the insulating film GI in a portionthereof which is superposed on the gate signal line GL.

This semiconductor layer AS constitutes a semiconductor layer of thethin film transistor TFT, and a drainelectrode SD1 and a sourceelectrode SD2 are formed on the top surface of the semiconductor layerAS, thereby forming a MIS type transistor having a reverse-staggeredstructure, which uses a part of the gate signal line GL as its gateelectrode.

The drain electrode SD2 and the source electrode SD1 are formed at thesame time as, for example, the drain signal line DL. Specifically, thedrain signal line DL is formed to extend in the y direction in FIG. 3;and, at this time, the source electrode SD2 is formed by extending apart of the drain signal line DL onto the top surface of thesemiconductor layer AS, and the source electrode SD1 is formed in aportion which is spaced apart from the drain electrode SD2 by a distancecorresponding to the channel length of the thin film transistor TFT.

The source electrode SD1 is disposed so as to be connected to the pixelelectrode PX via a protective film PSV, which will be described later,and is slightly extended toward the middle of the pixel area to form acontact portion CN.

The protective film PSV, which is made of, for example, a resin film (ora stacked structure in which a SiN film, SiN and a resin film arestacked in that order), is formed to cover the thin film transistor TFTand other elements on the surface of the transparent substrate SUB1 onwhich the thin film transistor TFT is formed in the above-describedmanner. This protective film PSV is formed chiefly in order to preventthe thin film transistor TFT from coming into direct contact with theliquid crystal.

A plurality of pixel electrodes PX, which are disposed to as to extendin the y direction and to be juxtaposed in the x direction in FIG. 3,are formed on the top surface of the protective film PSV, and thesepixel electrodes PX are formed so that the pixel electrodes PX and thecounter electrodes CT are alternately arranged with a space beinginterposed between each of the counter electrodes CT and the adjacentones of the pixel electrodes PX.

The pixel electrodes PX are constructed to be electrically connected inthe pattern wherein they are connected in pairs in an area which issuperposed on the counter voltage signal line CL, and the pixelelectrodes PX are connected to the source electrode SD1 of the thin filmtransistor TFT via a contact hole TH1, which is formed in the protectivefilm PSV.

Accordingly, a video signal from the drain signal line DL is supplied tothe pixel electrodes PX via the thin film transistor TFT, which isdriven by the supply of a scanning signal from the gate signal line GL.In addition, the pixel electrodes PX are arranged to òcause electricfields to be generated between the respective pixel electrodes PX andthe adjacent ones of the counter electrodes CT, to each of which asignal which serves as a reference is to be supplied.

The capacitance element Cstg is formed between the connection portionsof the respective pairs of pixel electrodes PX and the counter voltagesignal line CL, and the capacitance element Cstg has the function ofenabling a video signal to be stored in the pixel electrodes PX for acomparatively long time after the thin film transistor TFT is turnedoff.

Each of the pixel electrodes PX that extend in the y direction in FIG. 3is formed to have a zigzag shape such that it is extended from one endtoward the other end in a state where it is bent first in a θ direction(with respect to the y direction in FIG. 3), then in a −θ direction(with respect to the y direction in FIG. 3), and again in the θdirection (with respect to the y direction in FIG. 3). The counterelectrodes CT are bent similarly to the pixel electrodes PX and areformed in a pattern in which, if either the pixel electrodes PX or thecounter electrodes CT are shifted in the x direction in FIG. 3, bothelectrodes PX and CT can be superposed on one another.

The reason why the pixel electrodes PX and the counter electrodes CT areformed in according to the above-described pattern is that thisembodiment adopts a so-called multi domain scheme in which domains areformed so that the directions of the electric fields to be generatedbetween the pixel electrodes PX and the counter electrodes CT differfrom domain to domain, thereby canceling variations in color tone whichoccur when the display area is viewed in different directions withrespect to the display surface of the liquid crystal display device.

The counter electrodes CT (CT2) positioned on opposite sides (rightwardand leftward) of the pixel areas differ in a pattern from the othercounter electrodes CT (CT1); that is, each of the counter electrodes CT(CT2) has a side that extends in parallel with the adjacent drain signalline DL and a comparatively large width with respect to the othercounter electrodes CT (CT1).

These counter electrodes CT2 prevent light leakage by reducing the gapsbetween the respective counter electrodes CT2 and the adjacent drainsignal lines DL, and they provide the shield functions of preventingelectric fields generated from the adjacent drain signal lines DL fromterminating at the pixel electrodes PX.

An alignment film ORI1, which also covers the pixel electrodes PX, isformed on the surface of the transparent substrate SUB1 on which thepixel electrodes PX are formed in this manner. This alignment film ORI1is a film which is in direct contact with a liquid crystal LC so as torestrict the initial alignment direction of the molecules of the liquidcrystal LC. The rubbing direction of the alignment film ORI1 is madecoincident with the direction of extension of the drain signal lines DLin the case of a p-type liquid crystal, or the direction of extension ofthe gate signal lines GL in the case of an n-type liquid crystal.

A black matrix BM is formed to separate adjacent pixels from one anotheron the liquid-crystal-side surface of the transparent substrate SUB2,which is disposed in opposition to the transparent substrate SUB1constructed in this manner, with the liquid crystal material LC beinginterposed therebetween. Color filters FIL for corresponding colors arerespectively formed in the apertures of the black matrix BM (that serveas substantial pixel areas, respectively).

An alignment film ORI2, which also covers the black matrix BM and thecolor filters FIL, is formed, and the rubbing direction of the alignmentfilm ORI2 is made coincident with that of the alignment film ORI1 formedon the transparent substrate SUB1.

In the above-described construction, both the pixel electrode PX and thecounter electrode CT may be formed of an opaque metal film made of, forexample, Cr (or a Cr alloy), but at least either one of the pixelelectrode PX and the counter electrode CT may also be formed of atransparent metal film made of, for example, ITO (INDIUM-TIN-OXIDE).

In addition, in the case where the pixel electrodes PX and the counterelectrodes CT are formed of a transparent metal, the so-called apertureratio of each pixel is improved to a great extent.

Construction of Driver Circuit

As shown in FIG. 1, each of the video signal driver circuits He isdisposed to lie between the liquid crystal display panel PNL (moreexactly, transparent substrate SUB 1) and the printed circuit board PCB,and, as described above, the input terminals IT are electricallyconnected to the respective terminals of the printed circuit board PCBvia the anisotropic conductive film ACF.

In this portion, connection has heretofore been provided by solder.However, in the recent trends toward far higher resolutions of liquidcrystal display devices, with an increase in the number of the outputterminals OT of each of the video signal driver circuits He, the lengthbetween input terminals IT becomes narrow.

As a result, the problem occurs that adjacent terminals are shorted bysolder which tends to spread horizontally during bonding of the videosignal driver circuits He to the printed circuit board PCB.

In addition, even if such a problem does not occur, in a case whereresidual solder exists between adjacent terminals, a short is liable tooccur when an external force is applied to the terminals or to a nearbylocation.

To solve these problems, the anisotropic conductive film ACF is used forthe connection between the input terminals IT of the video signal drivercircuits He and the respective terminals of the printed circuit boardPCB.

The conductive beads contained in the anisotropic conductive film ACFare made small in size so that when the video signal driver circuits Heare secured to the printed circuit board PCB via the anisotropicconductive film ACF by thermocompression bonding, the conductive beadsare prevented from electrically connecting terminals disposed adjacentto one another.

FIG. 5 is a graph showing a short defect ratio against the lengthbetween the terminals in a case where solder is used and in a case wherethe anisotropic conductive film ACF is used.

In the case where solder is used, when the length between the terminalsis 0.40 mm or less, the short defect ratio sharply increases(particularly when it is 0.32 mm or less, the short defect ratioremarkably increases), whereas, in the case where the anisotropicconductive film ACF is used, the short defect ratio only increasesextremely gently. From this fact, it is seen that when the lengthbetween the terminals is 0.40 mm or less (or 0.32 mm or less), it iseffective to use the anisotropic conductive film ACF. The term “lengthbetween terminals” as used herein represents the distance betweenmutually opposed sides of adjacent ones of terminals disposed inparallel with one another.

In addition, the connection between the input-terminals of the verticalscanning driver circuits V and individual terminals of a printed circuitboard PCB is provided via an anisotropic conductive film ACF.

Incidentally, in the following description of individual embodiments,reference will be made to the video signal driver circuits He by way ofexample, however, the invention can also be applied to the verticalscanning driver circuits V.

Embodiment 2

An important aspect of this embodiment is that the anisotropicconductive film ACF is being used for the connection between theterminals of the video signal driver circuits He and those of theprinted circuit board PCB in the case where the distance between theterminals of each of the video signal driver circuits He is 0.20 mm orless.

The embodiment constructed in this manner can, of course, serve theadvantage of Embodiment 1, and, in addition, it is capable of solving aproblem due to the misregistration of the video signal driver circuitsHe with respect to the liquid crystal display panel PNL.

Specifically, a misregistration of approximately 0.10 mm normally occursduring the positioning of the video signal driver circuits He withrespect to the liquid crystal display panel PNL. In the case whereindividual terminals of the video signal driver circuits He and those ofthe liquid crystal display panel PNL are connected by using solder oncondition that the length between such terminals is 0.20 mm or less, thesolder spreads horizontally in its molten state and short circuitsfrequently occur between these terminals.

Accordingly, in the case where the length between the terminals is 0.20mm or less, the above-described problem can be solved by using theanisotropic conductive film ACF for the connection between the videosignal driver circuits He and the liquid crystal display panel PNL.

Embodiment 3

An important aspect of this embodiment is that the connection betweenthe individual terminals of each of the video signal driver circuits Heand those of the printed circuit board PCB is provided via theanisotropic conductive film ACF, and the anisotropic conductive film ACFis separated for each of the video signal driver circuits He.Specifically, as shown in FIG. 6, the anisotropic conductive film ACFused for each of the video signal driver circuits He is physicallyindependent from those used for other adjacent ones.

The anisotropic conductive film ACF is, as described above, made of aresin film in which conductive beads are scattered. Thus, in the case ofa portion in which no conductive beads exist in the resin, defectivecontact occurs in the portion between terminals on one side of theanisotropic conductive film ACF and terminals on the other side.

In a case where such an anisotropic conductive film ACF is formed incommon with the individual video signal circuits He, not only the videosignal driver circuit He located where defective contact is discovered,but also all other video signal driver circuits He must be peeled. Thatis because the anisotropic conductive film ACF has the nature of athermally dissolutive adhesive. This leads to a decrease in workefficiency.

For this reason, the anisotropic conductive film ACF is separately usedfor each of the video signal driver circuits He in this embodiment.Accordingly, for example, if a defective contact occurs between aterminal of one of the video signal driver circuits He and a terminal ofthe printed circuit board PCB to which the one is to be connected, onlythe one video signal driver circuit He can be peeled, and a repair canbe made with a new anisotropic conductive film ACF, with the other videosignal driver circuits He remaining unchanged.

Accordingly, it goes without saying that one video signal driver circuitHe need not be assigned to one separate anisotropic conductive film ACF,and two or more video signal driver circuits He may be assigned to oneanisotropic conductive film ACF.

On the other hand, for the connection between each of the video signaldriver circuits He and the liquid crystal display panel PNL, oneanisotropic conductive film ACF is used in common with all the videosignal driver circuits He. In other words, it is preferable when therespective video signal driver circuits He are connected to the liquidcrystal display panel PNL in different portions of one anisotropicconductive film ACF. The reason for this is that it is wise to givepreference to work efficiency during the thermocompression bonding ofsemiconductor devices to a liquid crystal display panel via ananisotropic conductive film, because the liquid crystal display panel isformed of glass having a low coefficient of thermal expansion and therate of occurrence of defects is small.

However, even in the case of the connection between the video signaldriver circuits He and the liquid crystal display panel PNL, theanisotropic conductive film ACF may, of course, be separated similarlyto those used on the printed circuit board PCB.

Embodiment 4

An important aspect of this embodiment is that an anisotropic conductivefilm ACF, which provides connection between the terminals of the liquidcrystal display panel PNL and the video signal driver circuits He,differs in physical property from the anisotropic conductive film ACFwhich provides connection between the terminals of the printed circuitboard PCB and those of the video signal driver circuits He.

Specifically, as one example, the anisotropic conductive film ACF, whichprovides connection between the terminals of the printed circuit boardPCB and those of the video signal driver circuits He, is formed to havea lower melting point than the anisotropic conductive film ACF whichprovides connection between the terminals of the liquid crystal displaypanel PNL and those of the video signal driver circuits He.

Accordingly, it is possible to lower the temperature of thethermocompression bonding of the video signal driver circuits He to theprinted circuit board PCB via the anisotropic conductive film ACF,whereby it is possible to restrain any influence due to a largedifference in coefficient of thermal expansion between the printedcircuit board PCB and, the video signal driver circuits He.

As for the connection between the liquid crystal display panel PNL andthe video signal driver circuits He, the coefficient of thermalexpansion of the liquid crystal display panel PNL is low and correctionfor expansion can be easily made. However, the connection between theprinted circuit board PCB and the video signal driver circuits Heentails the problem that such correction is difficult, because of thelarge coefficient value of thermal expansion. By using this embodiment,an expansion of the pitch between terminals can be decreased duringthermal attachment, and this is able to prevent the occurrence of adefective connection due to the resultant deviation.

In this case, it is advantageous that, after connection has beenprovided between the liquid crystal display panel PNL and the videosignal driver circuits He, connection is provided between the videosignal driver circuits He and the printed circuit board PCB.

Assuming that the liquid crystal display device is manufactured inreverse order, there is a risk that the printed circuit board PCB ismelted by heat generated during the thermocompression bonding of theliquid crystal display panel PNL and the video signal driver circuitsHe. Even if no such melting occurs, the connection between the videosignal driver circuits He and the printed circuit board PCB via theanisotropic conductive film ACF may be damaged.

In addition, as another embodiment, the dispersion density of conductivebeads (the number of conductive beads per unit area) contained in theanisotropic conductive film ACF which provides connection between theterminals of the liquid crystal display panel PNL and those of the videosignal driver circuits He is made higher than the dispersion density ofconductive beads contained in the anisotropic conductive film ACF, whichprovides the terminals of the printed circuit board PCB and those of thevideo signal driver circuits He.

The output terminals of each of the video signal driver circuits He (theterminals located on the side of the liquid crystal display panel PNL)are formed to be large in number and small in width. Thus, in case theconductive beads of the anisotropic conductive film ACF are notuniformly scattered and the conductive beads do not exist in a portionof the anisotropic conductive film ACF, defective contact easily occursin this portion. For this reason, the quantity of conductive beadscontained in the anisotropic conductive film ACF, which providesconnection between the terminals of the liquid crystal display panel PNLand those of the video signal driver circuits He, is made larger.

On the other hand, the input terminals of each of the video signaldriver circuits He show a large extent of misregistration with respectto the terminals of the printed circuit board PCB. Assuming that thequantity of conductive beads to be interposed between the inputterminals of each of the video signal driver circuits He and theterminals of the printed circuit board PCB is increased in theanisotropic conductive film ACF, short circuits easily occur betweenadjacent terminals as the result of the misregistration, as well ashorizontal travels or aggregations of donductive beads duringthermocompression bonding. This is why the quantity of the conductivebeads of the anisotropic conductive film ACF located at the inputterminals of the video signal driver circuits He needs to be reduced.

In addition, as another embodiment, the conductive beads contained inthe anisotropic conductive film ACF, which provides connection betweenthe terminals of the liquid crystal display panel PNL and the terminalsof the video signal driver circuits He, are made smaller in size thanthose contained in the anisotropic conductive film ACF, which providesconnection between the terminals of the printed circuit board PCB andthose of the video signal driver circuits He.

The output terminals of each of the video signal driver circuits He (theterminals located on the side of the liquid crystal display panel PNL)are formed to be large in number and small in width. Accordingly, theconductive beads contained in the anisotropic conductive film ACF aremade small in size to correspond to the widths of the terminals.Assuming that the conductive beads are formed to be large in size, theprobability that the conductive beads are disposed between opposedterminals becomes low, and there is a risk that defective contactoccurs.

On the other hand, the conductive beads contained in the anisotropicconductive film ACF, which provides a connection between the inputterminals of the video signal driver circuits He and the terminals ofthe printed circuit board PCB, are made large in size; and, as shown inFIG. 7, which is a cross-sectional view taken along line VII-VII of FIG.1, after thermocompression bonding, a conductive bead CB is deformedinto an oval shape, so that the area of contact between opposedterminals can be increased.

Since the liquid crystal display device is constructed to supplyelectric power from the printed circuit board PCB to the video signaldriver circuits He, this is extremely advantageous in terms ofcharacteristics to lower the resistance at such a terminal connectionportion in this manner.

Embodiment 5

This embodiment relates to the sizes of the conductive beads containedin the anisotropic conductive film ACF, which provides the connectionbetween the input terminals of the video signal driver circuits He andthose of the printed circuit board PCB.

As shown in FIG. 8, a conductive film CL is formed as an interconnectionpattern on the surface of the printed circuit board PCB, and aninsulating film IN is formed, which is opened in the area of a terminalpart of the printed circuit board PCB.

This insulating film IN is made of a film-like sheet stuck to theprinted circuit board PCB, and has a thickness of approximately 50 μm.

The size of the conductive bead CB contained in the anisotropicconductive film ACF is set to be not smaller than the film thickness ofthe insulating film IN.

Accordingly, the conductive bead CB of the anisotrepic conductive filmACF disposed in the opening of the insulating film IN, which exposes theterminal part, has a vertex portion fully projected from the surface ofthe insulating film IN, whereby it is possible to achieve the advantagethat connection is reliably provided between the conductive bead CB anda terminal of the video signal driver circuit He.

In addition, the terminals of the printed circuit board PCB areconstructed to be supplied with electric power, and by taking intoaccount the fact that the conductive beads of the anisotropic conductivefilm ACF are, as described above, deformed into oval shapes by thethermocompression bonding of the video signal driver circuits He, sothat the connection resistance between opposed terminals can be madefully small, it is also possible to determine the sizes of theconductive beads CB to be sizes large enough to provide reliableconnection between the terminals of the printed circuit board PCB andthose the video signal driver circuits He.

Embodiment 6

This embodiment provides a construction in which the anisotropicconductive film ACF is used for the connection between the inputterminals of the video signal driver circuits He and the terminals ofthe printed circuit board PCB, and the surfaces of the respectiveterminals of the printed circuit board PCB are plated with, for example,gold (Au).

As described previously, the terminals of the printed circuit board PCBare constructed to be supplied with electric power, and electriccurrents flow between the terminals of the printed circuit board PCB andthose of the video signal driver circuits He through locations, at eachof which mutually opposed terminals are in point contact with aconductive bead contained in the anisotropic conductive film ACF, asshown in FIG. 9. As a result, an excessive current concentration easilyoccurs at such a location.

In addition, since the distance between each of the terminals of theprinted circuit board PCB and an adjacent one is being increasinglynarrower, an electric current more easily flows through an electrolyticsolution such as water, which happens to be present between suchterminals, so that the terminals of the printed circuit board PCB aremore easily corroded by electrolytic corrosion. Accordingly, in thisembodiment, a gold (Au) layer incapable of being easily oxidized(denoted by sign PL in FIG. 9) is formed on the surface of each of theterminals of the printed circuit board PCB, thereby preventing thisproblem and ensuring the reliability of the connection.

From this fact, it is seen that the material of the layer formed on thesurface of each of the terminals of the printed circuit board PCB is notnecessarily limited to Au and may also be another material, such as anITO film that is incapable of being easily oxidized. In addition, itgoes without saying that at least each of the terminals of the printedcircuit board PCB may be formed of any of the above-described materials.

Embodiment 7

In this embodiment, terminals TM of the printed circuit board PCB are,as shown in FIG. 10, disposed in two rows in a so-called staggeredarrangement, in which each of the terminals of the first row is locatedat a position between adjacent ones of the terminals of the second row.Accordingly, it goes without saying that the respective input terminalsof the video signal driver circuits He are also arranged to correspondto the terminals of the printed circuit board PCB.

According to this arrangement, even if the terminals are disposed closeto one another, it is possible to avoid an arrangement in which mutuallyadjacent terminals (each of the terminals of the first row and a closestone of the terminals of the second row) are disposed with their sidesbeing opposed to each other.

This arrangement makes it possible to restrain the occurrence ofelectrolytic corrosion between an arbitrary one of the terminals and anadjacent one, whereby, even if electrolytic corrosion occurs, progresstoward damage to a terminal can be retarded to a great extent.

That is to say, the mutually adjacent terminals are arranged in such amanner that one of the diagonal lines of the terminal of the first rowand the corresponding one of the diagonal lines of the terminal of thesecond row are arranged to be approximately coincident with each other,and the terminals of the first and second rows can be spaced fully apartfrom each other, because a distance is provided between the first-rowgroup of terminals and the second-row group of terminals. Accordingly,it is possible to restrain the occurrence of electrolytic corrosion.

For instance, even if electrolytic corrosion occurs, the electrolyticcorrosion proceeds from one corner of a terminal toward an oppositecorner, but the required distance (corresponding to the length of adiagonal line extending one corner of the terminal to an oppositecorner) is comparatively large. Accordingly, progress of the damage tothe terminal can be retarded to a great extent.

Incidentally, in the case of a construction in which individualterminals are arranged in only one row, the terminals are closelydisposed with a side of each of the terminal being opposed to a side ofan adjacent one.

In this case, if electrolytic corrosion occurs in any of the terminals,the electrolytic corrosion proceeds from one side of an adjacentterminal toward an opposite side. Since the width of each of theterminals is extremely small, progress of the damage to the adjacentterminal is advanced.

The above-described construction of Embodiment 7 also serves theadvantage that it is possible to prevent the easy occurrence of peelingof an insulating film which covers the portion between each of theterminals and an adjacent other one. As described previously, thisinsulating film is formed by sticking a film-like sheet to such aportion, and if the width of the portion between adjacent openings inthe insulating film is narrow, the insulating film easily peels in thatportion. For this reason, the construction of Embodiment 7 isadvantageous.

In addition, in this case, regarding the anisotropic conductive filmACF, which provides connection between the video signal driver circuitsHe and the first-row group of terminals and the second-row group ofterminals on the printed circuit board PCB, it is preferable to use oneanisotropic conductive film ACF, without using a plurality ofanisotropic conductive films ACF, which are separated for the individualvideo signal driver circuits He. If such a plurality of anisotropicconductive films ACF are used, there is a case where they easily formoverlaps and cause trouble, such as a defective connection.

As is apparent from the foregoing description, in accordance with theliquid crystal display device according to the invention, it is possibleto provide reliable connection between semiconductor devices and printedcircuit boards.

While we have shown and described several embodiments in accordance withthe present invention, it is understood that the same is not limitedthereto, but is susceptible of numerous changes and modifications asknown to those skilled in the art, and we therefore do not wish to belimited to the details shown and described herein, but intend to coverall such changes and modifications as are encompassed by the scope ofthe applied claims.

1. A display device comprising: a display panel; a printed circuitboard; and a semiconductor device of a film carrier type which isdisposed to lie between the display panel and the printed circuit boardand is mounted on a film carrier, terminals of the semiconductor devicebeing respectively connected by an anisotropic conductive film toterminals of the printed circuit board that are disposed in oppositionto respective terminals of the semiconductor device, each of theterminals of at least one of the film carrier and the printed circuitboard connected by the anisotropic conductive film being spaced apartfrom an adjacently disposed terminal by a distance of no greater than0.40 mm.
 2. A display device according to claim 1, wherein each of theterminals of at least one of the film carrier and the printed circuitboard connected by the anisotropic conductive film is spaced apart froman adjacently disposed terminal by a distance of no greater than 0.32mm.
 3. A display device comprising: a display panel; a printed circuitboard; and a semiconductor device of a tape carrier type which isdisposed to lie between the display panel and the printed circuit boardand is mounted on a film carrier, terminals of the film carrier beingrespectively connected to terminals of the printed circuit board by ananisotropic conductive film, each of the terminals of at least one ofthe film carrier and the printed circuit board connected by theanisotropic conductive film being spaced apart from an adjacentlydisposed terminal by a distance of no greater than 0.02 mm.
 4. A displaydevice comprising: a display panel; a printed circuit board; and aplurality of semiconductor devices of a film carrier type which aredisposed to lie between the display panel and the printed circuit boardand are respectively mounted on a film carrier, first terminals of eachof the film carrier being respectively connected to terminals of theprinted circuit board by a first anisotropic conductive film, whilesecond terminals of each of the film carrier are respectively connectedto terminals of the display panel by an anisotropic conductive film, thefirst anisotropic conductive film for connecting the first terminals ofeach of the film carrier to the terminals of the printed circuit boardbeing formed separately for at least each one of the semiconductordevices, the second anisotropic conductive film for connecting thesecond terminals of each of the film carrier to the terminals of thedisplay panel being formed in common with a plurality of the filmcarrier.
 5. A display device comprising: a display panel; a printedcircuit board; and a plurality of semiconductor devices of a filmcarrier type which are disposed to lie between the display panel and theprinted circuit board and are respectively mounted on a film carrier,first terminals of each of the film carrier being respectively connectedto terminals of the printed circuit board by a first anisotropicconductive film, while second terminals of each of the film carrier arerespectively connected to terminals of the display panel by a secondanisotropic conductive film, the first anisotropic conductive film forconnecting the first terminals of each of the film carrier to theterminals of the printed circuit board being formed separately for atleast each one of the film carrier, the second anisotropic conductivefilm for connecting the second terminals of each of the film carrier tothe terminals of the display panel being formed separately for at leasteach one of the film carrier.
 6. A method for manufacturing a displaydevice which includes a display panel, a printed circuit board, and asemiconductor device of a film carrier type which is disposed to liebetween the display panel and the printed circuit board and is mountedon a film carrier, the method comprising the steps of: connecting thedisplay panel to the semiconductor device by a first anisotropicconductive film; and connecting the semiconductor device to the printedcircuit board by a second anisotropic conductive film having a lowermelting point than the first anisotropic conductive film.
 7. A displaydevice comprising: a display panel; a printed circuit board; and asemiconductor device of a film carrier type which is disposed to liebetween the display panel and the printed circuit board and is mountedon a film carrier, terminals of the film carrier being connected toterminals of the printed circuit board by an anisotropic conductivefilm, conductive beads which are contained in the anisotropic conductivefilm being set to have sizes larger than a thickness of an insulatingfilm which exposes the terminals of the printed circuit board.
 8. Adisplay device comprising: a display panel; a printed circuit board; anda semiconductor device of a film carrier type which is disposed to liebetween the display panel and the printed circuit board and is mountedon a film carrier, terminals of the film carrier being connected toterminals of the printed circuit board by an anisotropic conductivefilm, surfaces of the terminals of the printed circuit board beingcovered with a material layer incapable of being easily oxidized.
 9. Adisplay device comprising: a display panel; a printed circuit board; anda semiconductor device of a film carrier type which is disposed to liebetween the display panel and the printed circuit board and is mountedon a film carrier, terminals of the film carrier being connected toterminals of the printed circuit board by an anisotropic conductivefilm, at least one of the terminals of the printed circuit board andsurfaces thereof being covered with Au.
 10. A display device comprising:a display panel; a printed circuit board; and a semiconductor device ofa film carrier type which is disposed to lie between the display paneland the printed circuit board and is mounted on a film carrier,terminals of the film carrier being connected to terminals of theprinted circuit board by an anisotropic conductive film, the terminalsof the printed circuit board being disposed in at least two rows, eachof the terminals of one of the two rows being located at a positionbetween adjacent ones of the terminals of the other of the two rows, theterminals of the film carrier which are connected to the respectiveterminals of the printed circuit board being arranged to correspond toan arrangement of the terminals of the printed circuit board.